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1. Field of the Invention
In addition to nematic and cholesteric liquid crystals, optically active tilted smectic (ferroelectric) liquid crystals have also been used recently in commercial display devices.
2. Description of Related Art
Clark and Lagerwall have been able to show that the use of ferroelectric liquid crystals (FLCS) in very thin cells results in opto-electrical switching or display elements which have response times which are faster by a factor of up to 1000 compared with conventional TN (xe2x80x9ctwisted nematicxe2x80x9d) cells (see, for example, EP-A 0 032 362). On the basis of this and other favorable properties, for example the possibility of bistable switching and the fact that the contrast is virtually independent of the viewing angle, FLCs are fundamentally highly suitable for areas of application such as computer displays.
The use of FLCs in electro-optical or fully optical components requires either compounds which form tilted or orthogonal smectic phases and are themselves optically active, or the induction of ferroelectric smectic phases by doping compounds, which, although forming such smectic phases, are not themselves optically active, with optically active compounds. The desired phase should be stable over the broadest possible temperature range.
In order to achieve good contrast in electro-optical components, a uniform planar alignment of the liquid crystals is necessary. Good alignment in the SA and S*C phase can be achieved, for example, if the phase sequence of the liquid-crystal mixture is, with decreasing temperature:
isotropicxe2x86x92N*xe2x86x92SAxe2x86x92S*C
The prerequisite is that the pitch of the helix in the N* phase is very large (greater than 10 xcexcm) or, even better, is fully compensated (see, for example, T. Matsumoto et al., Proc. of the 6th Int. Display Research Conf., Japan Display, Sep. 30-Oct. 2, 1986, Tokyo, Japan, pp. 468-470; M. Murakami et al., ibid. pp. 344-347). This is achieved, for example, by mixing the chiral liquid-crystal mixture having, for example, a left-handed helix in the N* phase with one or more optically active dopants which induce a right-handed helix, in such amounts that the helix is compensated.
Use of Clark and Lagerwall""s SSFLCD (surface-stabilized ferroelectric liquid-crystal display) effect for uniform, planar alignment furthermore requires that the pitch in the smectic C* phase is significantly greater than the thickness of the display element (Mol. Cryst. Liq. Cryst. 1983, 94, 213 and 1984,114, 151).
The optical response time xcfx84[xcexcs] of ferroelectric liquid-crystal systems, which should be as short as possible, depends on the rotational viscosity of the system xcex3 [mPas], the spontaneous polarization PS [nC/cm2] and the electric field strength E [V/m], in accordance with the equation   τ  ∼      γ                  P        s            ·      E      
Since the field strength E is determined by the electrode separation in the electro-optical component and by the applied voltage, the ferroelectric display medium must have low viscosity and high spontaneous polarization in order to achieve a short response time.
Finally, in addition to thermal, chemical and photochemical stability, a low optical anisotropy xcex94n and a low positive or preferably negative dielectric anisotropy xcex94xcex5 are required (see, for example, S. T. Lagerwall et al., xe2x80x9cFerroelectric Liquid Crystals for Displaysxe2x80x9d, SID Symposium, Oct. Meeting 1985, San Diego, Calif., USA).
The totality of these requirements can only be achieved by means of mixtures of a plurality of components. The base (or matrix) used are preferably compounds which if possible themselves already have the desired phase sequence Ixe2x86x92Nxe2x86x92SAxe2x86x92SC. Further components of the mixture are frequently added in order to lower the melting point and to broaden the SC and usually also the N phase, to induce optical activity, for pitch compensation and to match the optical and dielectric anisotropies; however, the rotational viscosity, for example, should if possible not be increased.
Ferroelectric liquid-crystal displays can also be operated by utilizing the DHF (distorted helix formation) effect or the PSFLCD effect (pitch-stabilized ferroelectric liquid-crystal display, also known as SBF=short pitch bistable ferroelectric effect). The DHF effect has been described by B.I. Ostrovski in Advances in Liquid Crystal Research and Applications, Oxford/Budapest, 1980, 469 ff., and the PSFLCD effect is described in DE-A 39 20 625 and EP-A 0 405 346. In contrast to the SSFLCD effect, utilization of these effects requires a liquid-crystalline material having a short SC pitch.
Fluorinated derivatives of phenanthrene for use in liquid-crystal mixtures are disclosed, for example, in DE-A 195 00 768.
However, since the development, in particular of ferroelectric liquid-crystal mixtures, in particular can in no way be regarded as complete, the manufacturers of displays are interested in a very wide variety of components for mixtures. Another reason for this is that only the interaction of the liquid-crystalline mixtures with the individual components of the display device or of the cells (for example the alignment layer) allows conclusions to be drawn on the quality of the liquid-crystalline mixtures too.
The object of the present invention was therefore to provide novel compounds which, in liquid-crystalline mixtures, are suitable for improving the property profile of these mixtures.
Surprisingly, it has been found that fluorinated phenanthrene derivatives of the formula (I) are particularly suitable for use in liquid-crystal mixtures.
Not Applicable
The invention therefore relates to Fluorinated phenanthrene derivatives of the formula (I) 
where the symbols and indices are defined as follows:
G1 is xe2x80x94CHxe2x95x90CHxe2x80x94 or xe2x80x94CH2CH2xe2x80x94;
X1, X2, X3 and X4, independently of one another, are H or F, with the provisos that
a) X1 and X2, and X3 and X4 are not simultaneously H
b) X1 and X2, and X3 and X4 are not simultaneously F
c) at least one X from this group is F;
Y1 and Y2, independently of one another, are H or F;
R1 and R2 are identical or different and are
a) a straight-chain or branched alkyl radical (with or without an asymmetrical carbon atom) having 1 to 20 carbon atoms, in which, in addition, one or more H atoms may be replaced by F and where
a1) one or more non-adjacent and non-terminal xe2x80x94CH2xe2x80x94 groups may be replaced by xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94COxe2x80x94Oxe2x80x94, xe2x80x94Oxe2x80x94COxe2x80x94, xe2x80x94Oxe2x80x94COxe2x80x94Oxe2x80x94 or xe2x80x94Si(CH3)2xe2x80x94, and/or
a2) one or more xe2x80x94CH2xe2x80x94 groups may be replaced by xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94Cxe2x89xa1Cxe2x80x94, cyclopropane-1,2-diyl, 1,4-phenylene, 1,4-cyclo-hexylene or 1,3-cyclopentylene, and/or
a3) the terminal xe2x80x94CH3 group may be replaced by one of the following chiral groups (optically active or racemic): 
R1 is alternatively hydrogen, xe2x80x94OCF3, xe2x80x94CF3, xe2x80x94CN, xe2x80x94F, xe2x80x94Cl, xe2x80x94OCHF2, xe2x80x94OCH2F, xe2x80x94CHF2 or xe2x80x94CH2F;
b) R1 is alternatively hydrogen, Cl or F;
R3, R4, R5, R6 and R7 are identical or different and are
a) hydrogen
b) a straight-chain or branched alkyl radical (with or without an asymmetrical carbon atom) having 1 to 16 carbon atoms, where
b1) one or more non-adjacent and non-terminal xe2x80x94CH2xe2x80x94 groups may be replaced by xe2x80x94Oxe2x80x94, and/or
b2) one or two xe2x80x94CH2xe2x80x94 groups may be replaced by xe2x80x94CHxe2x95x90CHxe2x80x94,
c) R4 and R5 together may alternatively be xe2x80x94(CH2)4xe2x80x94 or xe2x80x94(CH2)5xe2x80x94 if they are bonded to an oxirane, dioxolane, tetrahydrofuran, tetrahydropyran, butyrolactone or valerolactone system; with the proviso that R3 can only be hydrogen if R3is a substituent of one of the ring systems mentioned;
M1 is xe2x80x94COxe2x80x94Oxe2x80x94, xe2x80x94CH2xe2x80x94Oxe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94Cxe2x89xa1Cxe2x80x94, xe2x80x94CH2xe2x80x94CH2xe2x80x94COxe2x80x94Oxe2x80x94, xe2x80x94CH2CH2CH2CH2xe2x80x94, xe2x80x94CH2CH2CH2Oxe2x80x94 and mirror-image arrangements thereof; or a single bond;
A1 is 1,4-phenylene, in which one or more H atoms may be replaced by F, Cl and/or CN, 1,4-cyclohexylene, in which one or two H atoms may be replaced by CN and/or CH3 and/or F, naphthalene-2,6-diyl, in which one or more H atoms may be replaced by F, Cl and/or CN; or a single bond.
The provision of compounds of the formula (I) very generally considerably broadens the range of liquid-crystalline substances which are suitable, from various applicational points of view, for the preparation of liquid-crystalline mixtures.
In this connection, the compounds of the formula (I) have a broad range of applications. Depending on the choice of substituents, they can be used as base materials of which liquid-crystalline phases are predominantly composed; however, it is also possible to add compounds of the formula (I) to liquid-crystalline base materials from other classes of compound in order, for example, to modify the dielectric and/or optical anisotropy of a dielectric of this type and/or to optimize its threshold voltage and/or its viscosity.
The compounds of the formula (I) are particularly suitable, even when added in small amounts, for influencing the dielectric anisotropy (xcex94xcex5).
Utilizing this property, the compounds of the formula (I) according to the invention are particularly suitable for use in FLC mixtures operated in inverse mode. They are furthermore particularly suitable for use in mixtures based on ECB mode (electrically controlled birefringence). The compounds of the formula (I) are also particularly suitable for use in nematic and chiralsmectic mixtures developed for active matrix or super- TFT modes.
In a group of compounds which are particularly suitable for use in ferroelectric and ECB mixtures, the symbols and indices in the formula (I) have the following meanings:
G1 is xe2x80x94CHxe2x95x90CHxe2x80x94;
Y1 and Y2 are H;
X1, X2, X3 and X4 are F (with the abovementioned provisos);
R1 and R2 are preferably identical or different and are
a) a straight-chain or branched alkyl radical (with or without an asymmetrical carbon atom) having 1 to 18 carbon atoms, in which, in addition, one or more H atoms may be replaced by F and where
a1) one or more non-adjacent and non-terminal xe2x80x94CH2xe2x80x94 groups may be replaced by xe2x80x94Oxe2x80x94, xe2x80x94COxe2x80x94Oxe2x80x94, xe2x80x94Oxe2x80x94COxe2x80x94, xe2x80x94Oxe2x80x94COxe2x80x94Oxe2x80x94 or xe2x80x94Si(CH3)2xe2x80x94, and/or
a2) one xe2x80x94CH2xe2x80x94 group may be replaced by cyclopropane-1,2-diyl, 1,4-phenylene or trans-1,4-cyclohexylene;
R1 and R2 are particularly preferably identical or different and are
a1) a straight-chain or branched alkyl radical (with or without an asymmetrical carbon atom) having 1 to 16 carbon atoms, where
a2) one non-terminal xe2x80x94CH2xe2x80x94 group may be replaced by xe2x80x94Oxe2x80x94, and one or more H atoms may be substituted by F.
M1 is preferably xe2x80x94CH2CH2xe2x80x94, xe2x80x94CH2CH2CH2CH2xe2x80x94 or a single bond.
M1 is particularly preferably a single bond.
A1 is preferably 1,4-phenylene, trans-1,4-cyclohexylene or a single bond.
A1 is particularly preferably a single bond.
This group includes, for example, the compounds (In), (Io), (Ip) and (Iq) shown below.
In a group of compounds which are particularly suitable for use in nematic liquid-crystal mixtures for active-matrix or super-TFT applications, the symbols and indices in the formula (I) have the following meanings:
G1 is xe2x80x94CHxe2x95x90CHxe2x80x94;
Y1 is F;
Y2 is H;
X1 is H or F;
X2 is H or F;
X3 is H;
X4 is H;
R1 is H, Cl, F, CF3O, CH2FO, CF3 or a straight-chain alkyl radical having 1 to 5 carbon atoms;
R2 is a straight-chain alkyl or alkoxy radical having 1 to 5 carbon atoms;
M1 is a single bond;
A1 is a single bond.
This group includes, for example, the compounds (Ig), (Ih), (Ii), (Ik), (IL), (Im), (In), (Io), (Ip), (Iq), (Ir), (Is), (It) and (Iu) shown below.
The compounds according to the invention are prepared by methods known per se from the literature, as described in the standard works on organic synthesis, for example Houben-Weyl, Methoden der Organischen Chemie [Methods of Organic Chemistry], Georg-Thieme-Verlag, Stuttgart.
The preparation is carried out under reaction conditions which are known and suitable for said reactions. Use can also be made here of variants which are known per se, but are not mentioned here in great detail.
If desired, the starting materials can also be formed in situ by not isolating them from the reaction mixture, but instead immediately converting them further into the compounds of the formula (I).
The following schemes show by way of example a possible synthetic route for the compounds of the formula (I), although other processes are feasible and possible. 
a) Hxe2x80x94Cxe2x89xa1Cxe2x80x94TMS, HN(iPr)2, Pd(II)/Cu(I) catalyst; e.g. J. Organomet. Chem. 453 (1993) 2, C19
b) HN(iPr)2, Pd(O) catalyst; analogously to J. Organomet. Chem. 453 (1993) 2, C19
c) H2/catalyst (P. N. Rylander, Hydrogenation Methods, Academic Press, London, 1985, p. 53)
d) Photocyclization (e.g. J. Am. Chem. Soc. 84, 4361 (1962))
e) H2/Pd (C)
R8: corresponds to R2 or can be converted into R2 by suitable subsequent reactions
The 2,3,4-trifluorobromobenzene employed in Scheme 1 for the synthesis of (Ia) or (Ib) is commercially available; the synthesis of the 3-bromo-2-fluoro-R8-phenyl derivative is described below. At the stage of photocyclization of 1-(2,3,4-trifluorophenyl)-2-(2-fluoro-3-R8-phenyl)ethene, the (Z)-isomer is preferably employed; however, the (E)-isomer can also be employed since the (Z)-isomer is formed therefrom under the photocyclization conditions and can react in situ to form (Ia).
According to Scheme 2, the target structures (Ic), (Id), (Ie) and(If) can be obtained from 1-bromo-2,4,5-trifluorobenzene (commercially available) and the abovementioned 3-bromo-2-fluoro-R8-phenyl derivative. Analogously, Scheme 3 describes the synthesis of the target compounds (Ig), (Ih), (Ii) and (Ik) from 1-bromo-2,4-difluorobenzene, which is likewise commercially available.
The 1-bromo-2,3,4-trifluorobenzene mentioned at the beginning of Scheme 4 is commercially available; the reactions proceed essentially analogously to those already described in Schemes 1-3.
The 3,4-difluoroacetophenone required as starting material in Scheme 5 is also commercially available. The further conversion to the target products does not display any peculiarities deviating from the other synthetic routes. For the synthesis of the target compounds (Ip), (Iq), (Ir) and (Is), Scheme 6 starts from commercial 4-bromo-2-fluorophenol, which is converted into the corresponding methyl ether by standard methods (for example Williamson ether synthesis). At the stage of the target compound (Ip) or (Iq), the methyl group can be cleaved off (by standard methods, for example using hydrobromic acid/acetic acid). The resultant hydroxyphenanthrene. can be converted into the target compound (Ir) or (Is) by reaction with difluorocarbene generated in situ. Scheme 7 starts from commercial 4-bromo-2-chlorofluorobenzene, which makes the target compounds (It) and (Iu) accessible substantially analogously to the schemes described above. 
a) Hxe2x80x94Cxe2x89xa1Cxe2x80x94TMS, HN(iPr)2, Pd(II)/Cu(I) catalyst; e.g. J. Organomet. Chem. 453 (1993) 2, C19
b) HN(iPr)2, Pd(O) catalyst; analogously to J. Organomet. Chem. 453 (1993) 2, C19
c) H2/catalyst (P. N. Rylander, Hydrogenation Methods, Academic Press, London, 1985, p.53)
d) Photocyclization (e.g. J. Am. Chem. Soc. 84, 4361 (1962))
e) H2/Pd (C)
f) 1. LDA 2. R9xe2x80x94Br or 1. LDA 2. Rxe2x80x94CHO 3. H+4. H2 
R8: corresponds to R2 or can be converted into R2 by suitable subsequent reactions
R9: corresponds to R1 or can be converted into R1 by suitable subsequent reactions
R: corresponds to the R9 which is shorter by 1 carbon atom 
a) Hxe2x80x94Cxe2x89xa1Cxe2x80x94TMS, HN(iPr)2, Pd(II)/Cu(I) catalyst; e.g. J. Organomet. Chem. 453 (1993) 2, C19
b) HN(iPr)2, Pd(O) catalyst; analogously to J. Organomet. Chem. 453 (1993) 2, C19
c) H2/catalyst (P. N. Rylander, Hydrogenation Methods, Academic Press, London, 1985, p. 53)
d) Photocyclization (e.g. J. Am. Chem. Soc. 84, 4361 (1962))
e) H2/Pd (C)
f) 1. LDA 2. R9xe2x80x94Br or 1. LDA 2. Rxe2x80x94CHO 3. H+4. H2 
R8: corresponds to R2 or can be converted into R2 by suitable subsequent reactions
R9: corresponds to R1 or can be converted into R1 by suitable subsequent reactions
R: corresponds to the R9 which is shorter by 1 carbon atom 
a) Hxe2x80x94Cxe2x89xa1Cxe2x80x94TMS, HN(iPr)2, Pd(II)/Cu(I) catalyst; e.g. J. Organomet. Chem. 453 (1993) 2, C19
b) HN(iPr)2, Pd(O) catalyst; analogously to J. Organomet. Chem. 453 (1993) 2, C19
c) H2/catalyst (P. N. Rylander, Hydrogenation Methods, Academic Press, London, 1985, p.53)
d) Photocyclization (e.g. J. Am. Chem. Soc. 84, 4361 (1962))
e) H2/Pd (C)
R8: corresponds to R2 or can be converted into R2 by suitable subsequent reactions 
a) Hxe2x80x94Cxe2x89xa1Cxe2x80x94TMS, HN(iPr)2, Pd(II)/Cu(I) catalyst; e.g. J. Organomet. Chem. 453 (1993) 2, C19
b) HN(iPr)2, Pd(O) catalyst; analogously to J. Organomet. Chem. 453 (1993) 2, C19
c) H2/catalyst (P. N. Rylander, Hydrogenation Methods, Academic Press, London, 1985, p.53)
d) Photocyclization (e.g. J. Am. Chem. Soc. 84, 4361 (1962))
e) H2/Pd (C)
R8: corresponds to R22 or can be converted into R2 by suitable subsequent reactions 
a) Hxe2x80x94Cxe2x89xa1Cxe2x80x94TMS, HN(iPr)2, Pd(II)/Cu(I) catalyst; e.g. J. Organomet. Chem. 453 (1993) 2, C19
b) HN(iPr)2, Pd(0) catalyst; analogously to J. Organomet. Chem. 453 (1993) 2, C19
c) H2/catalyst (P. N. Rylander, Hydrogenation Methods, Academic Press, London, 1985, p.53)
d) Photocyclization (e.g. J. Am. Chem. Soc. 84, 4361 (1962))
e) H2/Pd (C)
f) 1. HBr/HOAc 2. CF2Cl2/base/phase-transfer catalyst
R8: corresponds to R2 or can be converted into R2 by suitable subsequent reactions 
a) Hxe2x80x94Cxe2x89xa1Cxe2x80x94TMS, HN(iPr)2, Pd(II)/Cu(I) catalyst; e.g. J. Organomet. Chem. 453 (1993) 2, C19
b)HN(iPr)2, Pd(0) catalyst; analogously to J. Organomet. Chem. 453 (1993)32, C19
c) H2/catalyst (P. N. Rylander, Hydrogenation Methods, Academic Press, London, 1985, p. 53)
d)Photocyclization (e.g. J. Am. Chem. Soc. 84, 4361 (1962))
e) H2/Pd (C)
R8: corresponds to R2 or can be converted into R2 by suitable subsequent reactions
In general, for the synthesis of the groups (xe2x80x94A1xe2x80x94M1), R1 and xe2x80x94CH2xe2x80x94R2, reference may be made, for example, to DE-A 23 44 732, 24 50 088, 24 29 093, 25 02 94, 26 36 684, 27 01 591 and 27 52 975 for compounds containing 1,4-cyclohexylene and 1,4-phenylene groups.
Dioxane derivatives are advantageously prepared by reaction of a corresponding aldehyde (or a reactive derivative thereof) with a corresponding 1,3-diol (or a reactive derivative thereof), preferably in the presence of an inert solvent, such as benzene or toluene, and/or in the presence of a catalyst, for example a strong acid, such as sulfuric acid, benzenesulfonic acid or p-toluenesulfonic acid, at temperatures from about 20xc2x0 C. to about 150xc2x0 C., preferably from 80xc2x0 C. to 120xc2x0 C. Primarily suitable reactive derivatives of the starting materials are acetals.
Some of said aldehydes and 1,3-diols and reactive derivatives thereof are known and some can be prepared without difficulty by standard methods of organic chemistry from compounds known from the literature. For example, the aldehydes are obtainable by oxidation of corresponding alcohols or by reduction of nitriles or corresponding carboxylic acids or derivatives thereof, and the diols are obtainable by reduction of corresponding diesters.
Compounds in which an aromatic ring is substituted by at least one F atom can also be obtained from the corresponding diazonium salts by replacement of the diazonium group with a fluorine atom, for example by the methods of Balz and Schiemann.
As far as the linking of ring systems to one another is concerned, reference may be made, for example to the following:
N. Miyaura, T. Yanagai and A. Suzuki in Synthetic Communications 11 (1981), 513-519, DE-C 39 30 663, M. J. Sharp, W. Cheng, V. Snieckus in Tetrahedron Letters 28 (1987) 5093; G. W. Gray in J. Chem. Soc. Perkin Trans II 1989, 2041 and Mol. Cryst. Liq. Cryst. 172 (1989) 165, 204 (1991) 43 and 91; EP-A 0 449 015; WO-A 89/12039; WO-A 89/03821;
EP-A 0 354 434 and EP-A 0 694 530 for the direct linking of aromatics and heteroaromatics; DE-A 32 01 721 for compounds containing xe2x80x94CH2CH2xe2x80x94bridges, and Koji Seto et al. in Liquid Crystals 8 (1990) 861-870, for compounds containing xe2x80x94Cxe2x89xa1Cxe2x80x94 bridging members.
Esters of the formula (I) can also be obtained by esterification of corresponding carboxylic acids (or reactive derivatives thereof using alcohols or phenols (or reactive derivatives thereof, by the DCC method (DCC=dicyclohexylcarbodiimide) or analogously to DE-A 44 27 198. The corresponding carboxylic acids and alcohols or phenols are known and can be prepared analogously to known processes.
Particularly suitable reactive derivatives of said carboxylic acids are the acid halides, especially the chlorides and bromides, furthermore the anhydrides, for example also mixed anhydrides, azides or esters, in particular alkyl esters having 1-4 carbon atoms in the alkyl group.
Particularly suitable reactive derivatives of said alcohols and phenols are the corresponding metal alkoxides or phenoxides, preferably of an alkali metal, such as sodium or potassium.
The esterification is advantageously carried out in the presence of an inert solvent. Particularly suitable solvents are ethers, such as diethyl ether, di-n-butyl ether, THF, dioxane or anisole, ketones, such as acetone, butanone or cyclohexanone, amides, such as DMF or hexamethylphosphoric triamide, hydrocarbons, such as benzene, toluene or xylene, halogenated hydrocarbons, such as tetrachloromethane, dichloromethane or tetrachloroethylene, and sulfoxides, such as dimethyl sulfoxide or sulfolane.
Ethers of the formula (I) are obtainable by etherification of corresponding hydroxyl compounds, preferably corresponding phenols, where the hydroxyl compound is advantageously first converted into a corresponding metal derivative, for example into the corresponding alkali metal alkoxide or alkali metal phenoxide by treatment with NaH, NaNH2, NaOH, KOH, Na2CO3 or K2CO3. This alkali metal compound can then be reacted with the corresponding alkyl halide, alkyl sulfonate or dialkyl sulfate, advantageously in an inert solvent, such as acetone, 1,2-dimethoxyethane, DMF or dimethyl sulfoxide, or alternatively with an excess of aqueous or aqueous-alcoholic NaOH or KOH, at temperatures from about 20xc2x0 to 100xc2x0 C.
Regarding the synthesis of specific radicals R1 and R2 reference may additionally be made, for example, to
EP-A 0 355 008 for compounds having silicon-containing side chains,
EP-A 0 292 954 for optically active compounds containing an oxirane ester unit,
EP-A 0 263 437 for optically active compounds containing an oxirane ether unit,
EP-A 0 361 272 for optically active compounds containing a dioxolane ester unit,
EP-A 0 351 746 for optically active compounds containing a dioxolane ether unit,
U.S. Pat. No. 5,051,506 for optically active compounds containing a 2,3-difluoroalkoxy unit,
U.S. Pat. No. 4,798,680 for optically active compounds containing a 2-fluoroalkoxy unit,
U.S. Pat. No. 4,855,429 for optically active compounds containing an xcex1-chlorocarboxyl unit,
EP-A 0 552 658 for compounds containing cyclohexylpropionyl radicals, and
EP-A 0 318 423 for compounds containing cyclopropyl groups in the side chain.
The invention also relates to the use of compounds of the formula (I) in liquid-crystal mixtures, preferably smectic and nematic mixtures, particularly preferably ferroelectric and nematic mixtures. Particular preference is given to use in ferroelectric liquid-crystal mixtures operated in inverse mode and in nematic liquid-crystal mixtures for xe2x80x9cactive matrixxe2x80x9d, super-TFT-IPS and/or ECB applications.
The invention furthermore relates to liquid-crystal mixtures, preferably smectic and nematic mixtures, particularly preferably ferroelectric and nematic mixtures, comprising one or more compounds of the formula (I). The smectic or nematic liquid-crystal mixtures according to the invention are preferably suitable for use in electro-optical displays, in the case of nematic-mixtures particularly for xe2x80x9cactive matrix displaysxe2x80x9d and xe2x80x9cin-plane switching displaysxe2x80x9d (IPS-LCDs), in the case of smectic liquid-crystal mixtures for ECB (electrically controlled birefringence) displays, for electroclinic displays and chiral tilted smectic (ferroelectric and antiferroelectric) displays.
The liquid-crystal mixtures according to the invention generally comprise from 2 to 35 components, preferably from 2 to 25 components, particularly preferably from 2 to 20 components.
They generally comprise from 0.01 to 80% by weight, preferably from 0.1 to 60% by weight, particularly preferably from 0.1 to 30% by weight, of one or more, preferably 1 to 10, particularly preferably 1 to 5, very particularly preferably 1 to 3, of the compounds of the formula (I) according to the invention.
Further components of liquid-crystal mixtures comprising compounds of the formula (I) according to the invention are preferably selected from known compounds having smectic and/or nematic and/or cholesteric phases. These include, for example:
derivatives of phenylpyrimidine, as described, for example, in WO-A 86/06401 and U.S. Pat. No. 4,874,542,
meta-substituted aromatic compounds having a six-membered ring, as described, for example, in EP-A 0 578 054,
silicon compounds, as described, for example, in EP-A 0 355 008,
mesogenic compounds having only one side chain, as described, for example, in EP-A 0 541 081,
hydroquinone derivatives, as described, for example, in EP-A 0 603 786,
phenylbenzoates, as described, for example, in P. Keller, Ferroelectrics 58 (1984), 3, and J. W. Goodby et al., Liquid Crystals and Ordered Fluids, Vol. 4, New York, 1984, and
thiadiazoles, as described, for example, in EP-A 0 309 514.
Examples of suitable chiral, non-racemic dopants are the following:
optically active phenylbenzoates, as described, for example, in P. Keller, Ferroelectrics 58 (1984), 3, and J. W. Goodby et al., Liquid Crystals and Ordered Fluids, Vol. 4, New York, 1984,
optically active oxirane ethers, as described, for example, in EP-A0 263 437. and WO-A 93/13093,
optically active oxirane esters, as described, for example, in EP-A 0 292 954,
optically active dioxolane ethers, as described, for example, in EP-A 0 351 746,
optically active dioxolane esters, as described, for example, in EP-A 0 361 272,
optically active tetrahydrofuran-2-carboxylic esters, as described, for example, in EP-A 0 355 561, and
optically active 2-fluoroalkyl ethers, as described, for example, in EP-A 0 237 007, EP-A 0 428 720 and U.S. Pat. No. 5,051,506.
Preferred further components of FLC mixtures employed in inverse mode are the following:
phenanthrene derivatives of the formula (II) 
fluoropyridines of the formula (III) 
difluorophenylene derivatives of the formula (IV) 
meta-substituted aromatic compounds of the formula (V) 
4-cyanocyclohexyls of the formula (VI) 
1,3,4-thiadiazoles of the formula (VII) 
where the symbols and indices have the following meanings:
X1 and X2 are identical or different and are, independently of one another, CH, CF or N;
Y is F, CF3 or R;
R and Rxe2x80x2 are identical or different and are, independently of one another, as defined for R1 and R2 in the formula (I);
A and M are identical or different and are, independently of one another, as defined in the formula (I), and
a, b, c and d are identical or different and are, independently of one another, 0 or 1, with the proviso that the compounds can contain not more than four ring systems and, with the exception of the formula (II), must contain at least two ring systems.
Suitable further constituents of nematic or chiral nematic liquid-crystal mixtures according to the invention are, for example,
4-fluorobenzenes, as described, for example, in EP-A 494 368, WO 92/06 148, EP-A 460 436, DE-A 4 111 766, DE-A 4 112 024, DE-A 4 112 001, DE-A 4 100 288, DE-A 4 101 468, EP-A 423 520, DE-A 392 3064, EP-A 406 468, EP-A 393 577 and EP-A 393 490,
3,4-difluorobernzenes, as described, for example, in DE-A 4 108 448, EP-A 507 094 and EP-A 502 407,
3,4,5-trifluorobenzenes, as described, for example, in DE-A 4 108 448 and EP-A 387 032,
4-benzotrifluorides, as described, for example, in DE-A 4 108 448,
phenylcyclohexanes, as described, for example, in DE-A 4 108 448.
The mixtures can in turn be used in electro-optical or fully optical elements, for example display elements, switching elements, light modulators, elements for image processing and/or signal processing or generally in the area of nonlinear optics.
The mixtures are furthermore suitable for field treatment, i.e. for operation in the quasi-bookshelf geometry (QBG) (see, for example, H. Rieger et al., SID 91 Digest (Anaheim) 1991, 396).
The ferroelectric liquid-crystal mixtures according to the invention are particularly suitable for operation in so-called inverse or xcfx84V(min) mode (see, for example, J. C. Jones, M. J. Towler, J. R. Hughes, Displays 1993, 14, No. 2, 86-93; M. Koden, Ferroelectrics 1996,179,121-129).
Liquid-crystalline mixtures comprising compounds of the general formula (I) are particularly suitable for use in electro-optical switching and display devices (displays). These displays are usually constructed in such a way that a liquid-crystal layer is enclosed on both sides by layers which are usually, in this sequence starting from the LC layer, at least one alignment layer, electrodes and a limiting plate (for example of glass). In addition, they can contain spacer!, adhesive frames, polarizers and, for color displays, thin color-filter layers. Other possible components are antireflection, passivation, compensation and barrier layers and electric non-linear elements, such as thin-film transistors (TFTs) and metal-insulator-metal (MIM) elements. The structure of liquid-crystal displays has already been described in detail in relevant monographs (see, for example, E. Kaneko, xe2x80x9cLiquid Crystal TV Displays: Principles and Applications of Liquid Crystal Displaysxe2x80x9d, KTK Scientific Publishers, 1987).
The invention therefore furthermore relates to a switching and/or display device, preferably a smectic or nematic switching and/or display device, in particular a ferroelectric switching and/or display device, containing a liquid-crystal mixture comprising one or more compounds of the formula (I). In devices which contain a nematic liquid-crystal mixture, active matrix displays and in-plane switching displays (IPS-LCDs) are preferred.
In devices which contain a smectic liquid-crystal mixture, ECB (electrically controlled birefringence) displays, electroclinic displays and chiral tilted smectic (ferroelectric or antiferroelectric) displays are preferred.
Such displays can be used, for example, as computer displays or in smart cards.
A ferroelectric switching and/or display device according to the invention is preferably operated in normal or inverse mode.
Ferroelectric switching and/or display devices operated by multiplex addressing can be operated, inter alia, in two different modes, so-called normal mode or so-called inverse mode (xcfx84V(min) mode). The difference between the two is in the addressing scheme and in the different requirements made of the dielectric tensor of the FLC material, i.e. of the FLC mixture. An overview is given, for example, by J. C. Jones et al. in Displays 1993, 14, No. 2, 86-93, referred to below as xe2x80x9cJonesxe2x80x9d, and in M. Koden in Ferroelectrics 1996, 179, 121-129, and the literature cited therein.
The switching characteristics of an FLC device can generally be represented by a diagram in which the driving voltage (V) is plotted on the horizontal axis and the width of the addressing pulses (xcfx84, time) is plotted on the vertical axis (see, for example, Jones, FIGS. 4, 8, 10 and 11).
A switching curve is determined experimentally and divides the V,xcfx84 area into a switching region and a non-switching region. The pulse width usually shortens when the voltage is increased. This behavior characterizes so-called normal mode (see, for example, Jones, FIG. 4).
In suitable materials, however, the VT curve has a minimum (at voltage V(min)), as shown, for example, in Jones in FIGS. 8, 10 and 11. This minimum arises from superposition of dielectric and ferroelectric twist. FLC devices are operated in inverse mode if the sum of the row and column driving voltages in the operating temperature range is greater than the minimum on the Vxcfx84 curve, i.e. V(row)+V(column) greater than V(min).
In the present application, various documents are cited, for example in order to illustrate the technical background to the invention. All these documents are expressly incorporated herein by way of reference.
The invention likewise relates to novel ethyne derivatives of the formula 
in which:
R10 is an alkyl or alkoxy radical having 1 to 16 carbon atoms,
R11 is H if Z6 is F; or 
in which:
a) Z1 is F; Z2 is alkyl or alkoxy having 1 to 16 carbon atoms; Z3, Z4 and Z5 are H; Z6 is F
b) Z1, Z2 and Z3 are F; Z4 and Z5 are H; Z6 is F
c) Z1 and Z3 are F; Z2 is H; Z4 and Z5 are H; Z6 is F
d) Z1 and Z3 are F; Z2 is H; Z4 and Z5 are H; Z6 is H
e) Z2 and Z3 are F; Z1 is H; Z4 and Z5 are H; Z6 is H
f) Z1, Z2 and Z3 are F; Z4 and Z5 are H; Z6 is H
g) Z1 is H; Z2 is Cl; Z3 is F; Z4 and Z5 are H; Z6 is H.
In the preferred process for the preparation of the compounds of the formula (I), they have a key function since on the one hand they can be hydrogenated to the corresponding ethene derivatives (which are themselves photocyclized; see above Schemes 1-7) in very good yields and high purities without the production of substantial amounts of by-products, and on the other hand are accessible in high yields and very good purities in a convergent reaction which easily facilitates homologization.
It has been found that this reaction sequence 1-aryl-2-arylxe2x80x2-ethyne-1-aryl-2-arylxe2x80x2-ethenexe2x80x94photocyclization is not only particularly suitable for the phenanthrene derivatives according to the invention, but is also particularly suitable for the preparation of phenanthrene derivatives having a different substitution pattern of electronegative radicals (as described, for example, in U.S. Pat. No. 5,648,021 or DE-A 19524230 with still other preparation processes therein).
The invention likewise relates to boronic acid derivatives of the formula 
in which:
R12 is H or alkyl having 1 to 10 carbon atoms, preferably H, with the understanding that the cyclic anhydride which forms in the case where R12=H is likewise according to the invention. In the preparation of this compound, a mixture of boronic acid and the cyclic anhydride thereof is usually formed, but this does not cause problems either for Suzuki couplings or for oxidation to the phenol, since both the mixture and each of the individual components undergoes the relevant reactions.
The invention likewise relates to a process for the preparation of 3-bromo-2-fluorophenol starting from 3-bromo-2-fluorophenylboronic acid. Compared with other feasible processes (for example nucleophilic substitution of one of the bromine atoms of 2,6-dibromofluorobenzene), this process is distinguished by high regioselectivity, good yield and high purity.